EMI Glossary & Acronyms

Antenna
Electromagnetic waves are coupled through a transducer, from a transmitter to space and from space to a receiver. Antenna design parameters include: impedance, polarization, bandwidth, beamwidth, directivity, gain and radiation pattern.

Aperture
In a shielded enclosure an aperture is an opening that may become a source of leakage for electromagnetic energy. In designing for EMI an aperture should have a maximum dimension less than 1/20 wavelength of the highest frequency to avoid EMI emissions issues. The most common apertures in a shielded enclosure are: LEDs, joints, seams, switches and connectors.

Attenuation
Expressed in (dB) decibels, it is the amount of reduction or loss of energy expressed in voltage, current or power, in a device such as an attenuator, filter or shielded enclosure.

Bonding
The act of fixing two substrates together to create electrical conductivity between them The bond can occur from physical contact between conducting surfaces or by adding an electrical connection.

Conducted Emission (CE)
EMI (electromagnetic interference) that maybe generated in electronic devices and transferred through powerlines, I/O lines or control leads. It is coupled through conduction from one device to another.

Crosstalk
The coupling of conducted emission between pairs of wires, one which carries emission from a source and the other connected to a susceptible device. PCBs (printed circuit board, crosstalk is the interaction or interference between signals on two different electrical nets. Some relief can be had by clamshell packaging.

Current Probe
Is an EMI measuring sensor. They are used to measure conducted emission currents on signal lines and power leads and ca also locate and quantify ground loops.

Decibel (dB)
A logarithmic method for expressing power, voltage and current ratios and may be used for other electrical rations across the same or equal impedances.

dBuV/m = decibels (voltage level) referenced to 1 microvolt per meter; used for electric field intensity measurement.
dBuV/m/MHz = decibels referenced to 1 microvolt per meter per MHz; used for broadband field intensity measurement.

Electric Field (E)
The potential gradient of a radiated wave measured in volts/m.

Electromagnetic Compatibility (EMC)
The capability of equipment or systems to be used in their intended environment within designed efficiency levels without causing or receiving degradation due to unintentional EMI. EMC generally encompasses all of the electromagnetic disciplines.

Electromagnetic Disturbance (EMD)
Any electromagnetic phenomenon that may degrade the performance of equipment and/or system. NOTE: An electromagnetic disturbance may be an electromagnetic noise, an unwanted signal, or a change in the propagation medium itself.

Electromagnetic Environment (EME)
The total of electromagnetic phenomena existing at a given location. This includes all conducted and radiated emissions. The DoD definition: it is the sum of electromagnetic interference; electromagnetic pulse; hazards of electromagnetic radiation to personnel, ordnance, and volatile materials; and natural phenomena effects of lightning and static.

Electromagnetic Environmental Effects (EEE) or (E3)
As defined by the Department of Defense (DoD), there are many types of E3 that can affect the electromagnetic compatibility (EMC) of a system. This group of EMC disciplines is used to properly address the EMC environment over the system life cycle. The American National Standards Institute (ANSI C63.14) has been adopted by the DoD to serve as a standard dictionary for definitions commonly used pertaining to E3. This group includes the following: Electromagnetic Environment (EME), Electromagnetic compatibility (EMC), Electromagnetic Interference (EMI), Electromagnetic Vulnerability (EMV), Electromagnetic Pulse (EMP), Hazards of Electromagnetic Radiation to Personnel (HERP), Hazards of Electromagnetic Radiation to Ordinance (HERO), Hazards of Electromagnetic Radiation to fuel (HERF), Lightning, Precipitation static, Electrostatic discharge (ESD), Emission Control.

Electromagnetic Field (EMF)
Condition produced in space by the joint interaction of oscillating electric and magnetic fields which move independently of the charges or poles from which they originate. Per Maxwell’s equations, a varying electric field produces a varying magnetic electric and vice versa. They are in phase and time quadrature. The cross product of the electric field upon the magnetic field produces the power density directional flow known as Poynting’s vector.

Electromagnetic Interference (EMI)
Any electromagnetic disturbance, phenomenon, signal, or emission that causes, or is capable of causing, undesired responses or degradation of performance in electrical or electronic equipment. EMI is characterized by the following categories for test and measurement purposes: 1. Conducted Emissions, 2. Radiated Emissions, 3. Conducted Susceptibility, 4. Radiated Susceptibility.

Electromagnetic Interference (EMI) Coupling Paths
EMI is produced by a source emitter and is detected by a susceptible victim via a coupling path. This may involve one or more of the following coupling mechanisms:
1. Conduction – electric current
2. Radiation – electromagnetic field
3. Inductive Coupling – magnetic field
4. Capacitive Coupling – electric field

Electromagnetic Pulse (EMP)
A broadband, high-intensity, short-duration burst of electromagnetic energy. In the case of nuclear detonations, the electromagnetic pulse signal consists of a continuous spectrum with most of its energy distributed throughout the lower frequencies of 3 Hz to 30 kHz. Such an intense single-pulse transient electromagnetic wave may be generated when a nuclear device is detonated or it may be generated by non-nuclear means. This intense wave may damage semiconductor components and signal processing circuitry that is found in electronic and electrical equipment.

Electrostatic Discharge (ESD)
A transfer of electric charge between bodies of different electrostatic potential in proximity or through direct contact.

Emitter
In EMI applications, this term applies to unintentional radiators, particularly those that are the source of interference. Otherwise, the term refers to the intentional radiators such as transmitter antennas.

Faraday Shield
A conductive material used to contain or control an electric field. It is placed between the primary and secondary windings of a transformer to reduce coupling capacitance and common-mode noise. The shield provides electrostatic shielding while passing electromagnetic waves. No ground is needed.

Fields (Near Field, Far Field)
Near the source, field properties are determined primarily by source characteristics. Far from the source, field properties depend mostly on the medium through which the field propagates.
Near to Far Field transition distance from the emitter:
r = l/2p (this is approx. 1/6 wavelength), for D < l/2
r = D2/2l, for D ³ l/2
r = 2l, often used at low frequencies.Where r is the near/far field interface distance (distance from antenna at which the E and H fields begin to decrease as 1/r), p is pi (3.14), and D is the length of the radiating antenna element (or aperture dimension) in terms of wavelength l.Note: Very close to the source, the field is called the induction field (reactive or quasi-static field, non-radiating E or H field may provide strong coupling at low frequency and close proximity to source). Farther away, it is called the fresnel region or near field (radiated field components decrease as 1/r3), and still farther from the source is the fraunhoffer region or far field (radiated field components decrease as 1/r). The far field wave impedance, E/H = 377 ohms (this is the characteristic impedance of the medium for air or free space).

Field Strength (FS)
The radiated voltage per meter (V/m) or current per meter (A/m) corresponding to electric (E) or magnetic (H) fields, respectively.

Grounding
The connection of an electric circuit or equipment to Earth or a conductive body of relatively large extent in place of Earth. The connection or bonding of an equipment case, chassis, bus, or frame to a conductive object or structure to ensure a common potential.

Immunity
The ability of equipment and/or system to perform without degradation in the presence of an electromagnetic disturbance.

Interference
The effect of unwanted energy due to one or more emissions upon the reception in a radio communication system, manifested by any performance degradation, misinterpretation, or loss of information, which could be extracted in the absence of such unwanted energy.

Noise
Undesirable electrical signals that are present in a circuit or equipment. This becomes interference if the result is a degradation in performance. Whenever possible, noise should be controlled at the source to avoid extensive interference problems.

Probe
Current Probe: A precision EMI measuring sensor which clamps onto a wire, wire pair, coaxial line, cable, harness or strap carrying current, intentional or interference. Snap-on current probes are used to measure the normal-mode current in a single wire or the common-mode current in a wire pair, coax or an entire bundle or harness. Current probes cover the 100 Hz to 1 GHz spectrum in two or three units.

Electric Field Probe: Small (usually 10-30 cm) monopoles feeding a FET amplifier for monitoring the E-field used often for diagnostic purposes. Some probes are passive and contain no amplifier. RF leakage sniffing at seams, gaps, slots, and apertures of a metal housing is one of many uses.

Radiated Emission (RE)
Desired or undesired electromagnetic energy that is propagated into or across space, either as a transverse electromagnetic wave or by capacitive or inductive coupling.

Radiated Susceptibility (RS)
The determination or measurement of a device’s capability to function in the presence of undesirable radiated EMI from external electromagnetic sources.

Radio Frequency (RF)
A frequency at which coherent electromagnetic radiation of energy is useful for communications. Radio frequencies are designated as very low: <30 kHz, low: 30 to 300 kHz, medium: 300 to 3,000 kHz, high: 3 to 30 MHz, very high: 30 to 300 MHz, ultrahigh: 300 to 3,000 MHz, superhigh: 3 to 30 GHz, and extremely high: 30 to 300 GHz.

Radio Frequency (RF) Compatibility
The ability of antenna-connected RF receiver and transmitter subsystems operating within a system to function properly without performance degradation caused by antenna-to-antenna coupling.

Radio Frequency Interference (RFI)
RFI is considered as part of the EMI spectrum, with interference signals being within the radio frequency (RF) range. This term was once used interchangeably with EMI.

Shielding Effectiveness
The relative capability of a shield to screen out undesirable electric and magnetic fields and plane waves. The measurement is the ratio of the signal received without the shield to the signal received inside the shield.

Shielding Gasket
A material that maintains shielding effectiveness across a seam or gap in an electronic enclosure. It is made from a variety of materials including fabric-wrapped foam, wire mesh, stamped metal, and elastomer.

Susceptibility
The inability of equipment/systems to perform without degradation in the presence of an electromagnetic disturbance. Susceptibility is often characterized as a lack of immunity. The threshold of susceptibility is the level of interference at which the test article begins to show a degradation in performance. This is often frequency-dependent.

Susceptibility Level
The electromagnetic noise environment in which a device or equipment can operate satisfactorily.